1. Field of the Invention
The present invention relates to a red-colored film having small optical anisotropy, in particular to a red-colored film having reduced anisotropy of amplitude transmittance in the directions of the film plane and film thickness perpendicular to the plane, respectively, and a red-colored composition suitably used for forming the red-colored film. The present invention also relates to a color filter and a liquid crystal display device using the red-colored film.
2. Description of the Related Art
Liquid crystal display devices have been valued for their space-saving, light weight and energy saving ascribed to their thin configuration, and applications of the display to a large-size television have been rapidly spreading. However, narrow viewing angle has been a great problem in conventional liquid crystal display devices.
Great factors affecting the viewing-angle dependency of the liquid crystal display device are birefringency of liquid crystal molecules and polarizer's own viewing-angle dependency.
Birefringency of the liquid crystal molecules refers to a difference in birefringences due to different crossing angles of elliptical refractive index of the liquid crystal molecule when the molecule is viewed frontally or aslant. To this problem, an improvement has been made for a most proven TN (twisted nematic) mode by disposing a retardation film, and has been also made in recent years by employing novel liquid crystal modes such as IPS (in-plane switching) mode and VA (vertical alignment) mode (Nakao and Wakemoto, Journal of Japanese Liquid Crystal Society, “Liquid Crystal”, 2(7), 153 (2003)).
Viewing-angle dependency of the polarizer is due to leakage of light since, although the light is quenched when two orthogonally placed polarizes are frontally viewed, the crossing angle of polarizing light axes becomes larger than 90° when viewed aslant. Using two sheets of biaxial films has been proposed for solving this problem (Yamada and Yamahara, Journal of Japanese Liquid Crystal Society, “Liquid Crystal”, 2(7), 184 (2003)).
However, higher level characteristics are required for making the screen size larger for use in televisions because, when a prospective angle increases, viewing-angle dependency is recognized as uneven color distribution on the screen.
Accordingly, suppression of viewing-angle dependency is being attempted with respect to components constituting the liquid crystal display other than the liquid crystal and polarizer. For example, it is proposed to reduce retardation by thinning the colored film with respect to the color filter that determines color characteristics of the liquid crystal display device (Jpn. Pat. Appln. KOKAI Publication No. 2000-136253).
However, since the red-colored film develops the color, unlike blue- and green-colored thin films, by transmission of the light near the slope at a longer wavelength side of the absorption band of the pigment contained in the film, anisotropy of the amplitude transmittance may be largely expressed by slight deviation of orientation and distribution of the pigment. Anisotropy of the amplitude transmittance becomes more evident in the red-colored film as the pigment is further finely divided for enhancing lightness and contrast ratio of the colored film. Accordingly, it has been a problem in a color filter comprising filter segments of red, blue and green colors that color leakage due to optical anisotropy of the red filter segment during black display causes color shift in a reddish direction.